1. Field of the Invention
This invention relates to a hydraulic braking pressure control system comprising a brake device; a hydraulic pressure control means for controlling the hydraulic pressure from a hydraulic pressure supply source in accordance with the amount of operation of an operating member; an auxiliary hydraulic pressure generating means including a working piston operatively connected to the operating member to advance in response to operation of the operating member and being slidably received in a housing with a front surface of the working piston facing a hydraulic pressure chamber; a hydraulic pressure transmitting means comprising a free piston slidably received in a cylinder body and having opposite ends facing an input hydraulic pressure chamber connected to the hydraulic pressure control means and an output hydraulic pressure chamber leading to the brake device, respectively; and an on-off valve interposed between the hydraulic pressure chamber in the auxiliary hydraulic pressure generating means and the brake device and adapted to be closed in response to an increase in output hydraulic pressure from the hydraulic pressure control means.
2. Description of the Relevant Art
Such a hydraulic braking pressure control system is known, for example, from Japanese Patent Publication No. 53263/86.
In this prior art hydraulic braking pressure control system, a hydraulic pressure controlled in the supply source hydraulic pressure control means is applied to the brake device via the hydraulic pressure transmitting means, and if the hydraulic pressure supply source fails for any reason, with the result that a satisfactory hydraulic pressure from the supply source cannot be ensured, a hydraulic pressure from the auxiliary hydraulic pressure generating means is applied to the brake device by opening the on-off valve.
However, if uneven wear of a pad occurs in the brake device, or if a vapor lock is produced in a hydraulic circuit between the hydraulic pressure transmitting means and the brake device, for example, the amount of fluid consumed is abnormally increased, with the result that a satisfactory hydraulic braking pressure may not be obtained in some cases, even if the hydraulic pressure supply source is in its normal state. In such a case, if a deficiency can be supplied from the auxiliary hydraulic pressure generating means, a satisfactory hydraulic braking pressure can be ensured. In addition, if a leak of fluid occurs on the brake device side in a condition in which the hydraulic pressure supply source is in its normal state, a satisfactory hydraulic braking pressure cannot be provided. Therefore, it is desirable that such a leak of fluid can be promptly detected.